A burner can be part of an industrial furnace having a process chamber in which a drying or heating process is performed. The burner can have a reaction zone communicating with the process chamber. In a premix burner, a mixture of fuel and oxidant, which is known as premix, is ignited and burned in the reaction zone to provide thermal energy for heating the process chamber.
Secondary fuel may be injected into the reaction zone through secondary fuel injectors. The thermal energy from the combustion of premix supplied by the burner can be sufficient to autoignite the secondary fuel. In order to dilute the secondary fuel, inert gases can be entrained into the secondary fuel stream prior to its combustion. Dilution of the secondary fuel prior to combustion can decrease the amount of localized hotspots during combustion. Decreasing the number of localized hotspots can decrease the amount of NOx production.